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Exposure: F-stops, Shutter Speed, and ISO

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“A photograph is a portrait painted by the sun.” Anonymous

The word photography means light writing. And that is what photography is- writing with light. There are many ways to manipulate the light that reaches your digital camera’s sensor, but the three main ways are through f-stops, shutter speed, and ISO.

F-stops

An f-stop is the measurement of the opening of the aperture. The aperture is the hole through which light enters the camera through the lens and is exposed to the sensor. The larger the f-stop value (i.e. f/22), the smaller the aperture and the less light is exposed to the sensor for a given amount of time. The smaller the f-stop value (i.e. f/1.4), the larger the aperture and the more light is exposed to the sensor for a given amount of time.

The f-stop value also determines depth of field. A smaller aperture has a deeper depth of field. These f-stop values are good for landscape shots or other scenes in which you want things in the foreground and the background to be in focus. A larger aperture has a shallower depth of field. These f-stop values are good for macro shots or other scenes in which you want a specific area to be in focus with things in the foreground or background to be out of focus.

The aperture works with other settings (shutter speed, ISO, etc.) to achieve proper exposure. You need to take into consideration how much available light is in the scene (if only using natural light) and how deep or shallow you want the depth of field to be. You may need to adjust the shutter speed to be faster or slower or adjust the ISO to be higher or lower.

Shutter Speed

Shutter speed determines the length of time that the shutter is open and exposes the camera’s sensor to light. The shutter is like a curtain that blocks the camera’s sensor from light until it is opened to take a picture. The longer amount of time that the shutter is open, the more light reaches the sensor for a given f-stop value. The shorter amount of time that the shutter is open, the less light reaches the sensor for a given f-stop value.

Shutter speeds vary from many thousandths of a second to several hours. Generally, you’ll need to use a tripod or steady the camera in some other way for shutter speeds that are slower than 1/125th or 1/200th of a second to avoid blurring. This will vary for different types of situations.

ISO

ISO determines how sensitive your camera’s sensor is to light. The lower the ISO value, the less sensitive the sensor is to light, the more light is needed to properly expose an image, and the less of a chance of digital noise occuring. The higher the ISO value, the more sensitive the sensor is to light, the less light is needed to properly expose an image, and the more of a chance of digital noise occuring.

Digital noise is specks of color and light in an image (usually in areas of shadow and solid color) that reduce the image’s detail and quality.

Photo by michaelk.

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